The present invention relates to weaving machines, and more particularly refers to a weaving machine provided with a device for correcting the distortion of the weft, that is a machine able to eliminate the aberrations of perpendicularity between the weft and warp.
As those skilled in the art know, a weaving machine comprises among other things, besides various structural and supporting parts, two temples consisting of rollers whose axis is parallel to the weft threads at the lateral edges of the cloth to be produced, and a smooth or threaded cylindrical cloth-deflecting bar, on which the said cloth presses, as soon as it is gathered, around an arc of contact before winding around a haul-off roll, in contact with which are one or more back-up rolls to draw the cloth off.
The said two temples perform the function of keeping the cloth taut during and after insertion of the warp threads, and to this end exert a pressure on the cloth, pressing it against a support surface. This arrangement of the parts means that the tension exerted on the cloth by the abovementioned haul-off roll due to the back-up rolls has effects which, in the areas where the said temples are installed, are very different from those which occur in the remaining areas of the cloth, that is in the central area.
In this area the cloth, coming under the said tension of the haul-off roll, stretches longitudinally, that is at right angles to the weft, to a considerably greater extent than in the areas near the temples, where the deformation of the cloth is opposed by the action of the temples themselves. As a consequence of this, the lines of the weft threads are not perfectly straight, and comprise a central section which is basically straight and then leads into two lateral sections which inflect towards the point on which the temples press.
This means that the lateral areas of the cloth are practically unusable because of the non-perpendicularity of the weft and warp with respect to each other. Because this lack of perpendicularity affects both lateral edges of the cloth for a length of at least 10 cm, a total of some 20 cm of the cloth has to be discarded, which, with current cloth sizes, corresponds to some 15% of the width of a fabric.
The economic damage caused by this problems, which is intrinsic to the modes of operation of a weaving machine, will be obvious.
In the present state of the art the only operation carried out to correct the distortions described above is to apply differential tensions to the cloth by a manual or other type of operation, and this operation means unacceptable additional costs. More importantly, with some types of cloth it is simply impossible to perform this operation: for example in cloths on which paints, resins or the like are spread in the course of processing, it is impossible to correct the distortions that occur during the actual weaving process.